1. Field of the Invention
The invention relates to an injector body for a fuel injection system, in which the injector body has a substantially cylindrically shaped valve chamber, into which fuel can be introduced at high pressure via an inlet bore, which discharges into an inlet opening in the valve chamber.
2. Description of the Prior Art
Injector bodies for fuel injection systems of the above type have a cylindrically shaped valve chamber, in whose wall the inlet opening of an inlet bore is located. The inlet bore communicates in turn with a pressure connection, at which the inlet line for fuel that is at high pressure discharges from a common rail. The high-pressure strength of the injector body depends on the geometry of the inlet region. The intersection of the inlet bore with the valve chamber represents the point that is subjected to the most severe load. One of the parameters here is the inlet angle of the inlet bore from the common rail into the injector body. If this angle between the center axis of the inlet bore and the longitudinal axis of the valve chamber is approximately 90xc2x0, then the stresses in the region of intersection can be kept slight. However, installation conditions at the cylinder head of an internal combustion engine do not always allow inlet angles of 90xc2x0.
The primary stress on the point of intersection is caused by the internal pressure applied. Under this internal pressure, the notch effect of the inlet bore in the region of intersection of the bores leads to high local notch tensile stresses in the circumferential direction of the valve chamber. Even if the inlet angle is optimal, the aforementioned tensile stresses are the limiting factor for the high-pressure strength of the injector body.
It is accordingly the object of the invention to reduce the notch tensile stresses in the circumferential direction of the valve chamber, in an injector body of the generic type in question, so that the injector body can be designed for higher pressure loads.
In the embodiment proposed according to the invention, the valve chamber, at least in the region of the inlet opening, has a bulge in its cross section in the circumferential direction adjacent to each inlet opening. Accordingly, there is an increase in volume in the valve chamber on both sides of the inlet opening. As a result, the valve chamber deforms, in the region of intersection of the bores, under internal pressure in such a way that because of the greater curvature in the region of the high-pressure intersection, bending pressure stresses and circumferential tensile stresses are superimposed on one another, which in turn reduces the notch tensile stresses in the region of intersection of the two bores (that is, the inlet bore and the valve chamber bore).
In this respect, bulges that are shaped symmetrically on both sides of the inlet opening are advantageous. Because of this symmetry, incident stresses can be compensated for optimally.
If the inlet angle (the angle between the center axis of the inlet bore and the longitudinal axis of the valve chamber) is 90xc2x0, then the bulges proposed according to the invention in the valve chamber cross section are advantageously located in a plane that is perpendicular to the longitudinal axis of the valve chamber. In the longitudinal direction of the valve chamber, the bulge extends at least across the region of the inlet opening. At inlet angles other than 90xc2x0, it may be advantageous for the plane in which the bulges are located to be oriented in the same way as the inlet bore, so that the center line of the inlet bore passes through this plane. Usually, however, it is sufficient, and simpler from a production standpoint, to place the bulges with a cross section perpendicular to the longitudinal axis of the valve chamber.
The valve chambers, which in most cases are shaped cylindrically, accordingly have a circular cross section (perpendicular to the longitudinal axis of the valve chamber). The bulges according to the invention each extend, in the region of the inlet opening of the inlet bore, in the circumferential direction of the valve chamber adjacent to the inlet opening, so that the bulges bring about a departure from the circular cross section. It has been found that a major increase in strength ensues if a bulge extends at least as far as a plane that passes through the inlet opening and extends parallel to the longitudinal axis of the valve chamber. It is again especially advantageous in this respect if the bulges are disposed symmetrically to the inlet opening. If the bulges extend past the aforementioned plane, then the bending pressure stresses that occur under internal pressure in the region of the inlet opening can compensate even better for the incident notch tensile stresses.
In an embodiment in which the bulges proposed according to the invention extend as far as the aforementioned plane, which extends parallel to the longitudinal axis of the valve chamber and through the inlet opening, it is advantageous if the valve chamber cross section is continued uniformly as far as that plane; the diameter can then be equivalent to the maximum diameter of the valve chamber. In such an embodiment, it has been found that a further increase in strength can be attained if the inlet bore extends eccentrically relative to the valve chamber.